In the title molecule, C21H20ClN3OS, the tetracyclic system is close to planar [r.m.s. deviation = 0.110 (4) Å]. The dihedral angle between the quinoline ring system and the benzene ring is 178.3 (1)° and the angle between two (S-C=C-N) halves of the thiazine ring is 173.4 (1)°. In the crystal, molecules are arranged via- interactions [centroid-centroid distances = 3.603 (2)-3.739 (2) Å] into slipped stacks extending along [010]. Intermolecular N-HO hydrogen bonds link the amide groups of neighbouring molecules along the stack, generating a C(4) motif. The title compound shows promising antiproliferative and anticancer activity.

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